Papers by Keyword: Fatigue Crack Behaviour

Abstract: Al-Li alloys are characterized by a strong anisotropy in mechanical properties and
microstructure with respect to the rolling direction. Plates of 2198 Al-Li alloy were friction stir
welded by employing maximum rotation speed: 1000 rev/min and welding speed of 80 mm/min,
both in parallel and orthogonal directions with respect to the rolling one. The joints mechanical
properties were evaluated by means of tensile tests at room temperature. In addition, fatigue tests
performed with a resonant electro-mechanical testing machine under constant amplitude control up
to 250 Hz loading, were conducted in axial control mode with R(σmin/σmax)=0.33, for all the
welding and rotating speed conditions. The fatigue crack propagation experiments were performed
by employing single edge notched specimens.With the aim to characterize the weld performances,
both the microstructure evolution at jointed cross sections, related to the welding variables, and the
fractured surfaces were respectively analyzed by means of optical and scanning electron
microscopy.

Abstract: The fatigue behavior of metals is strongly governed by the grain size variation. As the
tensile strength, the fatigue limit increases with decreasing grain size in the microcrystalline regime.
A different trend in mechanical properties has been demonstrated in many papers for metals with
ultrafine (< 1 m) and nanocrystalline (< 100 nm) grain size in particular in the yield stress and
fatigue crack initiation and growth. The fatigue behavior of electrodeposited nanocrystalline Ni (20
and 40 nm mean grain size) and nanocrystalline Co (20 nm) has been analyzed in the present paper
by means of stress controlled tests. The monothonic mechanical properties of the materials were
obtained from tensile tests by employing an Instron 5800 machine by measuring the strain with an
extensometer up to 2.5% maximum strain. The strain gage specimen dimensions measured 20 mm
length and 5 mm width, all the specimens were produced by electro-discharge machining. The low
cycle fatigue tests were performed with specimens of the same geometry of the tensile ones in
tension-tension with load ratio R=0.25. The fatigue crack propagation experiments were carried out
by employing single edge notched specimens measuring 39 mm in length, 9.9 mm in width and
with an electro-discharge machined edge-notch of 1 mm. All the endurance fatigue and crack
propagation tests were performed at 10 Hz.

Abstract: The fatigue crack growth behavior of weld metal (WM), heat affected zone(HAZ) and base metal(BM) of Duplex Stainless Steel 2205(DSS) has been determined at high-frequency fatigue testing machine. The results show that the fatigue crack growth rate of WM is slowest and the ability to resist fatigue crack growth is highest in the three parts. Secondly, the sensitivity caused by the stress change of WM is the highest, followed by HAZ, and the BM is the weakest.